The present invention relates to improvements in anti-friction bearings and more particularly to a novel through hardened race insert defining at least one of the raceways for a bearing.
The present invention is designed to increase the so-called service life of ball and roller bearings. The term "life" as it is customarily applied to bearings means that period of service which is limited by fatigue phenomena. "Life" is generally measured in number of revolutions of the bearing or in number of hours of operation at a certain speed of rotation. Thus, each bearing assembly has a limited life period even when it is effectively protected, well lubricated, and otherwise properly handled. Under these circumstances all cause of damage are eliminated except one, the fatigue of the material due to repeated stress under rotation. The effect of this fatigue is the so-called flaking, which starts as a crack and develops into a spalled area on one or the other of the load carrying surfaces, that is, on the balls or rollers or the raceway. Therefore, fatigue is ultimately unavoidable but the number of revolutions the bearing may make before flaking starts is a function of the bearing load. The various types of bearing failure usually are centered in the contacting load carrying surfaces, that is, the balls or rollers or raceways. In some applications, the balls or rollers are easily replaceable. However, in most instances where the raceway surface of the inner and outer ring becomes defective due to fatigue, the entire assembly is discarded.
The present invention is designed to extend the "life" of bearing assemblies by providing an insert for at least one of the bearing rings forming the raceway of the bearing and which is a separable part of at least one of the bearing rings. In this manner when the raceway exhibits fatigue indicia, the race insert may be removed and replaced and thereby extend the useful service life of the other elements of the assembly. The invention contemplates modification of conventional bearing assemblies now in use to receive a raceway insert in accordance with the present invention. In addition to extending the useful life of a bearing assembly, the provision of a replaceable raceway insert provides certain economies in the cost of the overall assembly. For example, the insert may be made of a high grade bearing steel whereas the remainder of either the inner or outer ring may be made of a low grade, less expensive steel or a non-ferrous alloy. Furthermore, the low grade steel may be easier to machine and finish for example, particularly in the case where the inner and outer ring is designed for a special purpose, as for example, in applications where the bearing ring has a gear configuration on its annular surface opposite the raceway.
The concept of a raceway insert or a multi-layer bearing ring is not new per se. For example, in the bearing assembly illustrated in the Olson U.S. Pat., No. 3,099,073, issued July 30, 1963 for Method of Making Anti-Friction Bearing Assembly, the inner and outer raceways are defined by inserts which are seated in generally triangular-shaped channels forming part of an outwardly opening groove in the inner ring and a similarly shaped inwardly opening groove in the outer ring. In each ring, the inserts comprise a pair of axially spaced members firmly seated in the three sided corner portion of the opening in the ring by an annular keeper key disposed between the inserts and secured to the ring by a series of circumferentially spaced countersunk screws. The assembly of the inserts in the rings is comparatively complicated and involves careful attention to finishing procedures in order to maintain the close tolerences required for assembling the parts. In Columns 4 and 5 of the patent, the particular assembly method is described in detail. Thus, the end product is a highly specialized assembly which is comparatively costly to manufacture. Furthermore, as pointed out in the Olson specification, each raceway is comprised of a plurality of inserts assembled end-to-end and as a result, there are gaps or seams in the raceway surface which are objectionable particularly in high speed bearing applications. By contrast, the insert of the present invention is a continuous annular member and the pocket in the ring for the insert extends axially to one axial end face of the ring to facilitate assembly of the insert from an axial end face of the ring. The insert thus may be shrink fitted to the ring and accordingly, the confronting surfaces of the insert and the ring do not have to be maintained within the critical close tolerences as compared to the inserts of the Olson patent. Furthermore, in the present instance, the insert and pocket have complementary tapered axially extending surfaces to lock the parts against axial displacement when the bearing is under load thereby obviating the need for additional fastening elements such as the keeper key and countersunk screws of the Olson assembly.
The Knowles U.S. pat. No. 1,505,352, which issued Aug. 19, 1924 on an anti-friction bearing shows an assembly wherein the inner and outer rings are multipiece members. The anti-friction bearing illustrated is the type having two rows of rolling elements wherein the inner and outer rings for each of the rows is mounted in a sleeve-like casing or the like. The casing is in the form of a thin tubular sleeve having in the case of the inner ring a pair of radially directed flanges at its outer ends to support the bearing rings and in the case of the outer ring a central rib for spacing the two outer rings for each row of rolling elements. Knowles does not recognize the problem of raceway failure and does not disclose or suggest that the race rings are separable for replacement purposes. Furthermore, Knowles does not disclose or suggest a specific insert arrangement as proposed by the present invention or the easy and economical means for assembling the insert in an inner or outer ring of a bearing assembly.
Even though the concept of the present invention has application to all types of bearings, the invention is described herein in connection with a so-called X-type bearing. A typical X-type bearing assembly is illustrated in Messinger U.S. Pat. No. 3,361,501 issued Jan. 2, 1968 and as illustrated therein, both inner and outer race rings having confronting angularly disposed raceways which define an annular space therebetween for a plurality of rollers having cylindrical load carrying surfaces and a cage for guiding and circumferentially spacing the rollers in the annular space. The rollers are of a predetermined geometry having a diameter to length relationship so that when they are inserted in the annular space between the rings, the generally cylindrical load carrying surface of some of the rolling elements are oriented to carry a load application from one axial direction on the confronting opposite raceways of the inner and outer rings and other rollers are oppositely oriented so that they contact and carry load on the raceways of the inner and outer rings disposed 90.degree. to said first raceways. As noted above, the raceways tend to wear over a given period of use under load. Accordingly, the aim of the present invention is to provide a novel race insert illustrated herein for the inner ring of an X-type bearing which is of more durable construction and which is easy and economical to assemble to the inner ring and which is easily replaced when necessary. The race insert comprises a comparatively small part of the entire assembly, and thus, provides the advantage of easy replacement at a relatively low cost and extension of the usefulness of the major portion of the bearing assembly.